The invention relates to a method for processing a surface of an embossing tool, in which at least one surface is subjected to a first treatment step over the entire area to achieve a degree of gloss and there is at least one further step in selected areas to achieve a different degree of gloss.
Generic embossing tools are required in the wood-processing industry, especially for the production of wood composite boards. The visible surfaces of the wood composite boards are embossed with the aid of the embossing tools in such a way that a desired motif, preferably a realistic reproduction of a natural surface structure, can be produced. To this end, resin films, as an example, are put on the wood composite boards, which are preferably made of particle boards, and the resin films are subsequently pressed together with the wood composite boards with pressure and heat in hydraulic heating presses. The resin film liquefies during the pressing process with pressure and heat, and polycondensation takes place. The pressing time and temperature determine the degree of cross-linkage of the resins and their surface quality. After the pressing period ends, the resin achieves the desired degree of cross-linkage and is in a solid phase. The resin surface takes on the desired, realistic surface in this process because of the surface structure of the embossing tool. Thermosetting resins, for instance melamine resins, phenolic resins or melamine/urea resins, are used as the coating material. A structured, metallic pressed sheet, preferably sheet steel, is used as the embossing tool here to structure the surface. The embossing tools are additionally provided with a coating to improve the resistance to wear and separation characteristics of the metal surface. Embossing tools that were produced with the aid of digital printing technology are used in this process as a preference, so that the decor papers that are used can likewise be produced on a correct scale and with conforming patterns according to the digital printing process.
A perfectly matching arrangement of the decor paper and the embossing structure can consequently be achieved; substantially better results than in the case of the prior art can be obtained because of that.
Embossing tools in the form of pressed sheets or endless sheets are manufactured via the corresponding processing of the surface in the prior art and, in fact, via the production of a desired surface structure. In the past, the pretreated sheet was provided with a matrix for this purpose, for instance by means of a screen-printing method, so that the sheet can then be etched. The sheet is only etched in connection with this in the areas that are not covered by the matrix. Very precise processing and especially processing with conforming patterns are required in connection with this due to the pressed-sheet size that is used, in so far as the surface structure is produced in several work steps. All of the areas that are supposed to form the raised surface structure later on are covered over and over again by the mask in connection with this, so the surface will only be etched in the areas that can be directly corroded by the etching fluid. The etched areas then form the profile valleys of the desired structure; the surfaces are cleaned and the mask is removed after the end of the respective etching process. This procedure can be repeated several times; the precision in the case of screen-printing processes causes substantial difficulties as a rule for a perfectly matching application of further masks.
An alternative method involves the application of a photo-sensitive layer at first, which is then subjected to light exposure, and the pressed sheets or endless sheets are subjected to a rinsing process after the concluding development of the photo-sensitive layer, so only the parts of the photo-sensitive layer that constitute the mask for the subsequent etching process remain. The reproducibility of the masks produced in this way is very difficult and problematic, because the negative or positive that is used to illuminate the light-sensitive layer has to always be exactly arranged in the same position relative to the existing structure.
Several illumination and etching processes are therefore required to reproduce complicated, three-dimensional structures on the surface of the pressed sheet or the endless sheet, for instance. Even the smallest deviations will lead to substantial displacements of the structures due to the fact that extremely large format pressed sheets are involved. The reproducibility of the application of the mask is therefore especially associated with substantial difficulties in the case of the photographic process for obtaining a high level of replication precision. The difficulties can get worse when a three-dimensional structure has to be obtained via several illumination and etching processes that are required one after the other and there is a necessity of applying several masks one after the other for this and of carrying out an etching process between each instance of mask application. The production of pressed sheets or endless sheets is very complex and cost-intensive because of the precise positioning that is required and the number of corresponding masks that is required. The results that can be obtained are, moreover, very heavily dependent upon the processes that are used; extensive handling has to be taken into consideration due to the size of the pressed sheets or endless sheets.
As an alternative, the production of a mask with the press of a button via the application of wax instead of a screen printing process is known from the prior art. The wax that is applied is chemically resistant to the etching means that are used in connection with this, so etching can be done in the areas in which the surface is not covered by the wax. To this end, a spray head is used that sprays the wax onto the surface and that can be moved along an x and y axis, in order to replicate the required structure. The use of wax to apply a matrix has turned out to be disadvantageous, however, because the wax can only be removed from the surface again with difficulty and the required cleaning work is very cost-intensive. The costs that arise because of this and the dissolution of a wax matrix have lead to a situation in which other digitalized printing techniques are required. As an example, the application of a UV lacquer with the aid of a printing head onto the surface of the embossing tools to be processed, especially pressed sheets or endless sheets, is known.
The special advantage of the digitalized printing technique involves the fact that nearly identical masks can be applied over and over again to existing structures, and several etching processes to obtain a deep structure, for instance, can therefore be carried out one after the other in a perfectly matching way.
A process for applying coatings to surfaces in which a nozzle head is used and the individual nozzles are driven by control signals is known from DE 102 24 128 A1, for example. The nozzle head can either be used over the surface, or the surface to be treated is moved vis-a-vis the nozzle head. A UV lacquer that is cured via illumination with UV light after the application to the surface is preferably used in connection with this.
Regardless of the form in which the structuring of the surfaces of the pressed sheets or endless sheets was done, they will be subjected to several cleaning processes and can additionally be coated with a nickel, brass or copper layer that is subsequently refined with further metallic coatings. The surface gets a desired degree of gloss and a required surface hardness with the metallic coatings. The degree of gloss is responsible for the different shadings and color reflections that the pressed structure here receives after the pressing of the materials to be processed with the aid of the pressed sheets or endless sheets.
Furthermore, to improve the visual effect, there was a proposal to provide partial areas of the surface with different metallic coatings to vary the degree of gloss. Desired shading effects can be obtained with this measure.